140 THE BOOK OF A NATURALIST 



insect-catching organ, a decoy, a tactile organ, and, 

 in some mysterious way, an organ of intelligence. 

 And, after all, it is none of these things, and the 

 way is still open for fresh speculation. 



I have on numberless occasions observed the 

 common pit-viper of southern South America, 

 which is of a sluggish disposition, lying in the sun 

 on a bed of sand or dry grass, coiled or extended at 

 full length. Invariably, on approaching a snake of 

 this kind, I have seen the tongue exserted ; that 

 nimble, glistening organ was the first, and for 

 some time the only sign of life or wakefulness in 

 the motionless creature. If I stood still at a dis- 

 tance of some yards to watch it, the tongue would 

 be exserted again at intervals ; if I moved nearer, 

 or lifted my arms, or made any movement, the 

 intervals would be shorter and the vibrations more 

 rapid, and still the creature would not move. Only 

 when I drew very near would other signs of excite- 

 ment follow. At such times the tongue has scarcely 

 seemed to me the " mute forked flash " that 

 Ruskin calls it, but a tongue that said something, 

 which, although not audible, was clearly understood 

 and easy to translate into words. What it said or 

 appeared to say was : "I am not dead nor sleeping, 

 and I do not wish to be disturbed, much less 

 trodden upon ; keep your distance, for your own 

 good as well as for mine." In other words, the 

 tongue was obtruded and vibrated with a warning 

 purpose. 



Doubtless every venomous serpent of sluggish 



